We have a credit application form hosted on SFDC Sites. A sales rep creates the credit app record, which triggers an email to be sent to the prospective customer. A link in the email takes them to the application on the SFDC site.
As of the Spring '21 release (this Saturday), an unauthenticated site user won't be able to edit a record they don't own. Since the credit app is owned by the sales rep, that's a problem.
Our current solution involves using Identity licenses, and having the customer log into our e-commerce site, on which they already have an account. That site passes them over to SFDC, where we use JIT provisioning to create a user record and sign them in. That's working fine, but only if we take the user into SFDC (to a Salesforce app). We haven't been able to figure out how to trigger authentication by going to the SFDC site instead.
I see a lot of articles about doing this with partner communities, and I have a feeling this is similar, but that's about as far as we've been able to get. Can someone point us in the right direction?